From the Group to the Individual: What Can be Learned from Migratory Behaviour

By taking the analysis of population renewal as subject of study, demography has deliberately positioned itself in a context that privileges the analysis of aggregate values: the `stock' of individuals is modified both in terms of volume and structure by the `stream' of births, deaths and all the other events which intervene in the movements of populations. Understanding these streams involves dealing with behaviour patterns which enable the individual to emerge from under the mass of statistics: the increasing use made of data from surveys based on biographical reconstitutions reveals more clearly than ever the existence of a microdemography alongside, or in complement to, a macrodemography. This dual aspect is not specific to demography and, in fact, affects all of the social sciences. Mark Blaug, for example, when referring to the coexistence of a microeconomy and a macroeconomy, underlines the fact that this creates "a kind of intellectual schizophrenia in which the techniques of either approach do not entirely cover the domain of the other. This situation is far from satisfactory and economists have been trying to bridge the gap between the consumer and the function of global consumption or between the investor and the factors involved in investment aggregates. The bridging of this gap, however, is only partially completed and the economics student must be prepared to use two different tool boxes". In this paper, Daniel Courgeau brings his contribution to this bridge-building by drawing a parallel between the analysis of individual data and aggregate data concerning migrations